1. Field of the Invention
This invention relates generally to structurally bonding structural elements together using adhesive placed in a specific shape/profile, and more particularly to advanced adhesive bond shape tailoring suitable to large composite primary structures subjected to cryogenic and ambient loading environments.
2. Discussion of the Related Art
Bonding of primary structures to withstand cryogenic temperatures and high stress launch environment is a fundamental requirement of deploying cryogenic primary structures. Cryogenic primary structures may include space structures made of composite materials. Failure of the bonds between structural elements can result in significant damage to the primary structures in an environment where repair is unfeasible.
Conventional bonds utilize a gusset plate to bond together composite tubes. Previously adhesive was placed between the gusset plate and composite tubes by simply spreading a thin layer of adhesive to the tube and then affixing the gusset plate. However, prior art techniques to spread the adhesive often resulted in bond areas having profiles that often caused delamination or separation of the composite tubes as well as undesired stress placed on the surface of the tubes due to either the profile of the perimeter of the bond area, improper location of the bond area proximate the cut end of the tubes, or non-uniform and improper thickness of the adhesive. The adverse effects, of the aforementioned prior art techniques of applying the adhesives, are exacerbated by the extreme cryogenic temperatures reaching 27 degrees Kelvin. Failure to properly control the application of the adhesive and resultant bond area will result in a significant reduction in the strength of the bond, strip away the upper layers of composite materials or otherwise induce delamination/separation and induce undue stress on the tubes when the structure is exposed to extremely low temperatures.
Adhesive thickness should be minimal as thick layers of adhesive may strip away the upper layers of composite mater when exposed to extremely low temperatures due to the mismatch in coefficient of thermal expansion of the materials. Accurately and precisely tailoring the shape of the adhesive applied onto the primary structures such that these needs are met significantly increases bond strength and reduces susceptibility to cryogenic temperatures and high stress environments.
Additionally, stress applied onto the bond may be significantly reduced by accurately shaping the adhesive with a large radius, particularly in areas of high stress. Finally, accurately and precisely tailoring the shape of the applied adhesive may reduce or prevent the need for clean out of areas in the primary structure that have limited access during the assembly of the primary structure.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for apparatus and methods to bond primary structures such that the bond survives cryogenic temperatures and demanding, high stress launch vehicle environment. There is also a need for improved apparatus and methods to accurately and precisely tailor the shape of adhesive applied onto primary structures to effectively bond these primary structures using a gusset plate.